Skip to main content

Hi All,

I didn’t get too far on the S-Trains list with my electrical questions, thought maybe I should try here. I am planning on powering my Xmas layout with a 13.8 VDC, 20 amp power supply, all my engines are DC. To control the trains on the 3 separate loops, I have PWM DC motor controllers rated at 10 amps, each with a 10 amp fuse which, I guess, protects the controller. With such high amperages, I’ve been told the trains will also need protection.

So, how much protection? Guessing again, I’m looking at 4 amp circuit breakers for each loop. I have no idea if this is a proper value for the circuit breakers – The engines are converted Flyer or SHS and AM DC, generally pulling lighted passenger cars.

Would like to hear if this setup is okay or not, because I don’t know if PWM DC motor controllers will harm the engines. I’m attaching the info for the controllers and circuit breakers with the hope that the more electronic savvy will comment.


Tom Stoltz

In Maine


Product features

·       Using imported high-power FET, the load current up to 10A

·       With fuse, to prevent short-circuit high current, causing burnout protection

·       With reverse power protection, to prevent damage to the module when the power is reversed

·       Original 63V / 1000uF large capacitor, to ensure the stability of the module

·       Potentiometers are equipped with nuts, you can use without adding other components

Product description

Important: This is DC motor controller, please make sure the input voltage is from DC power, do not use home 220V AC, otherwise it will burn out. The DC Motor Speed Controller allows controlling direction of a DC motor using a Pulse-Width-Modulated (PWM) DC voltage with a Duty Cycle fully adjustable from 10%-100%. The motor speed controller can provide a continuous current of 8A to your DC motor or other DC load. Specification: 100% brand new and high quality. Input supply voltage: DC 12V-40V The maximum output power: 400W The maximum continuous output current :8A The overload and short circuit protecting current is 10A Static Current:0.02 A ( Standby ) PWM frequency: 13kHz Duty Cycle adjustable: 10%-100% The operation environment temperature:-20℃-125℃ (L*W*H): 6cm x 5.5cm x 2.8cm/2.36"x 2.16"x1.10"(approx) Net weight: 69g NOTE:This can NOT be used to the BRUSHLESS motor. The controller is NOT reverse-polarity protected and will be damaged if connect the supply voltage with wrong polarity. Double check all connections before applying power and always turn off the power supply before making any wiring changes. Package Included 1*12V-40V 10A PWM DC Motor Speed Controller CVT Speed Switch Module


 DIYhz 4Amp Circuit Breakers Thermal Overload Switch Protector 88 Series Manual Push Button Reset with Quick Connect Terminals and Waterproof Button Cap 32VDC or 125/250VAC 4PCS

by DIYhz

  • Thermal circuit breakers (can also be used for 24-hour circuit protection)
  • Rating: 4A 125/250VAC/32VDC,Terminal width: 6.3mm(1/4")
  • Widely suitable For Automotive/Industrial/Marine And Many Other applications
  • Push-to-reset operation with black manual reset button,with a waterproof button cap to protect from bad weather.
  • The part is not designed for push on / push off manual switch operation, but the button pops out at overload and is reset by pushing back in.


Images (2)
  • PWM controller
  • 4 amp circut breaker
Original Post

Tom, I never saw this in the S gauge section. It is not clear what you mean by converted your engines. I am assuming you replaced the Gilbert open frame motors with can motors. If that is all you did (no electronics) then the 10A fuse should be adequate. You could add 5A breakers if you want. Think of it this way. The old Gilbert 4B's had 5A breakers and the 19B's had at least a 10A breaker. Since there were no sensitive electronics in the Gilbert engines these breakers were adequate. Even the Dallee electronic reversing boards were fine when powered from a 19B. I am not familiar with the DC supply/controller you have.

I ran the AM engines with the whistle and bell features from 19B's and never had any issues despite many shorts from running them into open turnouts.

Four illuminated Gilbert passenger cars pull one amp, six of the AM passenger cars are a little less than one amp. A double headed train with two can motors and six cars should be less than 3A so a 4A or 5A breaker is good unless there can be more than one train in a power district.

Hi Tom,

I don’t know where I came up with the 4A figure, but I thought I remembered it from somewhere. Like I said, I don’t know much about this end of the game. Maybe I’m thinking about DCC breakers? Anyway, I sounds like I should use a higher value. Would 10A be too much?

My converted Flyer engines are a mix. Some have been changed to can motors while others have a rectifier with the original open frame motors. Those are from before conversion can motors were available.

My concern with the controllers is the ‘PWM’. Even though the advertising states DC motor control, I don’t know if the PWM as any impact (like over-heating?) on the motor.

Thanks for your input,

Tom Stoltz

in Maine

Tom, there is nothing inherently bad about the PWM output as long as the DC waveform peak is 15V or less. At 100% duty cycle we do not want more than 15V to the Gilbert motors. You have two different beasts by also having the original 3 pole universal motors in some engines. The good news is these are very robust motors so the only way to damage them is over-voltage or stalling the motor with high current draw through it.

If you are planning to run these old Gilbert universal motors at very low speed using the PCM controller the motors will get hot but I doubt they will be damaged. There are a lot of harmonics in the PCM waveform and all they do is generate heat in the motor windings. Put a Gilbert tender with an AirChime Whistle in it on the track and listen to how loud it sounds, that is the harmonics. At low speed the back EMF is low (low motor impedance) so the short term current can be high, heating the armature windings. At higher operating speeds motor heating is not an issue because the armature impedance increases with speed.

A Gilbert steam engine with smoke using the original universal motor can draw as much as 2.5A; average when running is between 1.5A and 2A. Dual motor Alco PA's will draw up to 4A. Add on some passenger cars and the amperage can be over 4A. That is why I recommend a minimum 5A breaker. Also make sure your track is divided into blocks so that more than one train will not be continuously operating through the same breaker.

My layout has 10A breakers on the transformer outputs to the track. But the transformer has other fast acting electronic protection for all the sensitive Legacy electronics in the engines. The added protection is to limit fault currents and voltage spikes. Neither of these would be concerns in the simple DC engines you are running.

Thanks again Tom. Now to nit-pick this a bit more… These little circuit breakers are available in just about any amperage rating you want. 10A would be the same as the controller so which one would blow first? Would there be any advantage to using 9A breakers to also give some protection to the controllers? The controllers have old time glass tube fuses which would be a pain to change.

Or is this just not worth thinking about?

Tom Stoltz

in Maine

It would be best if the breaker on the output to the track tripped first. Picking breakers is a bit more complicated than just amperage rating. You want some that are "fast acting" so they are sure to trip before the link in the fuse melts. I would not want to replace those glass fuses every time there is a short on the layout. An 8A breaker should be fine with the engines you have.

Tom, I recommend you look at the Electrical forum. About the 18th topic down is a thread called The Case For Fast Acting Circuit Protection. I am hesitant to recommend a specific breaker since I do not use them, I use a ZW-L with all required protection built in. When I took a quick look at Amazon most of what was there are blade type breakers for automotive use.

Some of the posters prefer fast blow fuses rather than breakers, the recommendations in this thread are based on in user experience.

The fast blow glass fuses look like the ticket. I will go with 8A ones. Thank to everybody for the other suggestions, but the prices on the fancy, made for trains breakers are truly out of sight cost wise. Fuses and fuse blocks (holders) will be less than $20.00… enough to do 4 loops worth.

And another thanks to Tom for letting me know about the other forums. I had never looked beyond the train forums.

Tom Stoltz

in Maine

Tom,  fast blow glass fuses are what I still use - have for 14 years.  Work great, just bit extra effort to “reset” (replace).  7A for S, 1-3A for n-HO.  Just thought in case you wanted a more convenient 21st century solution.  I buy them 50 at a time on Amazon.  Much less expensive than auto parts stores or electronics shops. Enjoy. Practice safe S.  

Ordered all (I hope) of the necessary parts for the control end of things and am starting the platform today.  Thanks to everyone for the info and I will post when I test the PWM controller.

Dave, I went with the 8A fuses but didn't find a 50 pack on Amazon.  There was a 100 pack, however the price was so cheap I was leery of them.  I ended up with buying 10 packs.

Tom Stoltz

in Maine


AmFlyer posted:

Tom, when you get it running let us know how the engines work with the PCM controller.

Finally got the PWM controllers hooked up and running… this is a Xmas layout, you know. I let them run for an hour without any heating that I could find. The heat sinks on the controllers didn’t even get warm. As for the trains, they run so silky smooth it is amazing… and the slow speed -- Wow! I can make them barely crawl. This is so cool.

I feel the trains are quieter, much quieter. Is there any reason this could be true? There is one thing that is a little funny and strange though. On one of the loops my AM K4 headlight would blink at just one spot, every time – no hesitation in the engine movement, just a blink of the light. I figured it was a low spot or dirty track. When I switched to the regulated power supply it doesn’t blink any more… weird.

Tom Stoltz

Having fun, running trains, in Maine

A pulsed power supply can enable the engines to run slower. Since you are using DC the motors would tend to be quieter than with AC. Apparently the 13kHz of your controller does not cause any motor noise like the 60kHz "chopped" waveform of AC power supplies like the ZW-L. Nice to see it worked and the trains are running well.

Magnetic circuit breakers have faster reaction times than thermal breakers (you hope the thermal breaker heats and trips faster than your train electronics burn up).

Snapak breakers are suitable between the transformer and the trains.  I have been using instant trip breakers (PP11-0-10.0).  Look at the part number code tables at the end of the data sheet and you can easily see if a part in stock is instant or fast trip:

Shop around.  The prices shown on the river site are excessive.  I had to order mine from a power protection specialty shop and wait several weeks to get a decent price.


Add Reply

OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
Link copied to your clipboard.